The present invention relates to a device capable of increasing the rotation speed of a magneto motor and, more particularly, to a plurality of sets of magnetic sensors provided in a magneto motor to sense rotary pole variation of a permanent magnet of the rotor and let exciting coils of the stator have different conduction time differences and torsion coefficients KT of different strengths so that the same motor can generate various kinds of different rotation speeds.
To manufacture an electromotor of high operational efficiency, an appropriate value of the torsion coefficient KT must be designed and matched with the operational range of the electromotor, as illustrated with the following formulas.
E=KExc2x7xcexa9
KE=Bxc2x7Dxc2x7Lxc2x7Z/2
T=KTxc2x7Ia
KT=Bxc2x7Dxc2x7Lxc2x7Z/2
wherein E is the counter electromotive force voltage (volt), T is the output torsion (Nxe2x88x92m), KE is the counter electromotive force coefficient, KT is the torsion coefficient, xcexa9 is the rotation speed of the armature (rad/sec), Ia is the armature current (ampere), B is the magnetic flux density of the gap (gauss), D is the outer diameter of the armature (cm), L is the superimposed thickness (cm), and Z is the total number of turns of conductors.
As can be seen from the above formulas, the counter electromotive force coefficient KE equals the torsion coefficient KT, and the counter electromotive force coefficient KE is inversely proportional to the rotation speed of the armature xcexa9. Therefore, for a fixed counter electromotive force voltage E, if the normal rated rotation speed of the armature xcexa9 is lower, the value of the counter electromotive force coefficient KE will be relatively higher, while if the normal rated rotation speed of the armature xcexa9 is higher, the value of the counter electromotive force coefficient KE will be relatively lower. If a motor is designed to have a higher normal rated rotation speed of the armature xcexa9, the value of the torsion coefficient KT will be relatively lower so that the torsion T (T=KTxc2x7Ia) can only be increased with a higher armature current Ia if the motor is operated at a lower rotation speed. If a motor is designed to have a higher torsion coefficient KT, the motor will not accomplish a higher normal rated rotation speed xcexa9 because KT=KE and E=KExc2x7xcexa9.
The present invention can let a motor have a higher torsion coefficient KT. Moreover, the present invention can switch to magnetic sensors sensing angle in advance to let the armature of the motor generate the effect of weak magnetic control, hence reducing the magnetic flux density of the armature gap. From the above formulas KE=Bxc2x7Dxc2x7Lxc2x7Z/2 and E=KExc2x7xcexa9, because the magnetic flux density B of the armature gap decreases, the counter electromotive force coefficient KE consequentially decreases. Therefore, the rotation speed of the armature, xcexa9, will inevitably increase.
The torsion coefficient KT of the prior art motor is a single value. For a motor usually operating in the range of lower rotation speeds and sometimes operating in the range of higher rotation speeds (e.g., a light electric vehicle), in order to let the motor operate in the seldom work range of the highest rotation speed when necessary, because KE=KT, E=KExc2x7xcexa9, and T=KTxc2x7Ia, the torsion coefficient KT and the counter electromotive force coefficient KE must decrease for increasing the rotation speed xcexa9 to the seldom work range of the highest rotation speed if the counter electromotive force voltage E is fixed. Because the torsion coefficient KT decreases, and the motor usually operates in the range of lower rotation speeds, the armature current Ia must increase to increase the torsion T because T=KTxc2x7Ia. However, a too large Ia is not good to the operational efficiency of the motor. This can be known from the following formula.
P=I2xc2x7R
wherein P is the dissipated power of the coil of an electromotor, I is the armature current, and R is the impedance of the coil. Therefore, if the torsion of a motor is increased by increasing the armature current, the dissipated power of the stator coil will increase squarely, and heat will be generated in the impedance of the coil. The impedance of the coil will correspondingly rise due to the temperature rise of the metallic coil. This vicious circle will let the motor operate in an environment of high temperature, hence resulting in a worse output efficiency.
A stator portion of a conventional motor is formed by winding a single coil. Therefore, the torsion coefficient KT and the counter electromotive force coefficient KE thereof are consequentially constant values. If a motor is designed to have higher values of the KT and KE, the rotation speed of the armature, xcexa9, will decrease proportionally. In the present invention, a plurality of sets of magnetic sensors are provided in a magneto motor to sense rotary pole variation of a permanent magnet of the rotor. A set of magnetic sensors is provided at the position of the stator portion letting the difference between the conduction time of the stator""s exciting coil and the rotary pole variation time of the rotor be zero or lower so that the motor can generate the strongest or stronger torsion coefficient KT. Another set of magnetic sensors is provided at the position of the stator portion letting the difference between the conduction time of the stator""s exciting coil and the rotary pole variation time of the rotor be longer so that the motor can generate a phenomenon similar to weak magnet control. Detection signals of the magnetic sensors are controlled by a magnetic detection signal selection circuit, and are integrated to output a detection output signal to a motor drive and control circuit, which lets the stator portion and the magneto rotor portion generate armature reactions of different strengths.
The above weak magnetic control device capable of increasing the rotation speed of a motor when necessary can let the motor have a larger torsion coefficient KT. When a motor of larger KT value operates at lower rotation speeds, because the armature current Ia can be decreased proportionally (T=KTxc2x7Ia), the dissipated power of the stator coil of the motor will also decrease (P=I2xc2x7R), thereby reducing the working temperature of the motor and increasing the operational efficiency of the motor operating at lower rotation speeds.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: